Re: Modern Marshalls
For the OP, tubes and speakers matter with a Marshall.
The original Marshall circuit was designed back when tubes and the equipment it ran with were different (granted, that circuit has been fluffed out over the years with effects loops and things, but the core of it is based on a Fender Bassman circuit.). Matching all the elements around that as period-correct as possible gets you closer to that better tone you are wanting.
In my tube leftovers I had a Mullard 10M 12AX7. I put that in V1 of my SLX and with just that I had AC/DC, Deep Purple, Free, you name-it vintage rock (I also have Svetlana Winged C EL34 in the power section, still a touch bright/biting to me, but the V1 Mullard smoothed things notably). I loved my SLX again. I run mine through Celestion Vintage 30s and alternatively 25w Greenbacks. When I bought the SLX, it had Tesla EL34s in it (not sure who made the pre tubes then) but it was that same beautiful 60s/70s rock sound, not fizzy and not too bright, but chimy when clean. I could use the presence and treble as needed to match the guitar, not for solving amp sound problems.
One of my amps is a Fender Vibro-King........60w listing tubes:
Tubes: five 12AX7A (p/n 013341) two GT—6L6 GE (p/n 059778) one 6V6-GTA (p/n 023564)
Instead of an attenuator or cranking volume past 6 or 7......are there 1 or 2 good tubes that would have the tone break up at much earlier volume levels (like a 3 or 4)? Thanks for any advice.............and could the same be done for Marshalls that do not distort until things are way too loud? Thanks again....
(Seems like a thread hijack, but it's a really good question. Probably should branch this off to a new thread if it turns into several responses.) I recently got a KT77 to test in a small amp and while most EL34s start to break up @60% on the gain knob for me, the KT77s began this beautiful break up @30% on the gain knob and all of it was useful throughout the range (this is with 12AX7 pres and GZ34 rectifier). I'm thinking of trying the KT77s in my SLX next.
6L6s break up at the last 10-15% of the volume range for me, so they aren't the tubes to use for early break up in my experience. Another tube that gets beautiful break up at lower power is a 6V6, but you have to match rectifiers and pre tubes along with it to get it right. I don't know the Vibro-King circuit to know what you can safely substitute. But spec-wise it should be a great amp as is. I'm jealous. I couldn't get that one in my budget.